Method and apparatus of CT imaging with voltage modulation

ABSTRACT

A system and method of diagnostic imaging with reduced x-ray exposure to the scan subject during scanning includes acquiring a set of cardiac signals or other motion (cardiac mechanical motion or respiratory motion) related signals and determining and imaging profile therefrom. Pursuant to the imaging profile, voltage applied to an x-ray source is modulated to provide an energizing voltage during primary data acquisition stages and a reduced voltage during secondary or non-data acquisition stages. Voltage modulation repeats until sufficient data for image reconstruction has been acquired.

BACKGROUND OF THE INVENTION

The present invention relates generally to diagnostic imaging and, moreparticularly, to a method and apparatus of acquiring diagnostic imagingdata with voltage modulation to reduce radiation exposure.

Typically, in computed tomography (CT) imaging systems, an x-ray sourceemits a fan-shaped beam toward an object, such as a patient. The beam,after being attenuated by the scan subject, impinges upon an array ofradiation detectors. The intensity of the attenuated beam radiationreceived at the detector array is typically dependent upon theattenuation of the x-ray beam by the patient. Each detector element ofthe detector array produces a separate electrical signal indicative ofthe attenuated beam received by each detector element. The electricalsignals are transmitted to a data processing for subsequent imagereconstruction.

Reducing radiation exposure during a CT scan has always been a desiredgoal and is becoming increasingly important with the introduction ofmulti-slice CT scanning for patient screening, such as coronary arterycalcification scoring (CACS) tests and coronary artery imaging (CAI).For CACS tests, known multi-slice CT scanning systems often usestep-and-shoot scanning and EKG-based prospective gating techniques toeliminate radiation redundancy. That is, the x-ray source is on for onlya certain period during the heart cycle to emit radiation toward thescan subject and thereby allow acquisition of the data necessary for“step-and-shoot” scanning. To provide adequate coverage within a patientbreath holding time in accordance with a “step-and-shoot” scan, it iscustomary to use a relatively thick slice (for example, a slicethickness of 2.5 mm).

It is often desirable to use thinner slice thicknesses to improve imagequality and to use continuous patient feeding (helical scans) to improvecoverage and patient throughput without introducing redundant exposureduring CACS tests. This requires turning on the x-rays for the cardiacperiod when the heart has the least motion and turning off the x-raysfor the remainder of the heart cycle during a single, long helical scan.

It is also customary in coronary artery imaging for helical scanning andthin slice collimation (1.25 mm) to be used to provide good imagequality and adequate coverage. Patients are continuously fed along thepatient long-axis while the x-ray is on to provide continuous volumecoverage and full cardiac cycle imaging. However, it has been realizedthat not all cardiac phases in a cardiac cycle are equally important.Full image quality should be provided for those cardiac phases whenheart has the least motion. While images are needed for other phaseswhen the heart has greater motion to provide a complete picture for thecoronary artery imaging tasks, image quality may be compromised.

Another method to achieve these scanning modes is to reduce patientexposure to x-rays include modulating an x-ray tube current based on thecardiac cycle. This method has certain drawbacks, however, since thecooling time of the filament in the x-ray tube limits the modulationresponse resulting in increased patient exposure to x-rays.Additionally, the x-ray tube requires a minimum current in order tooperate.

Therefore, it would be desirable to design an apparatus and method foracquiring data for image reconstruction without unnecessary radiationexposure to the scan subject in completing the CACS tasks and withreduced radiation exposure to the scan subject in completing the CAItasks. It would be further desirable to design such a system withoutsacrificing image quality or subject throughout.

BRIEF DESCRIPTION OF THE INVENTION

The present invention is a directed method and apparatus for acquiringimaging data with voltage modulation to reduce radiation exposure to thescan subject that overcomes the aforementioned drawbacks.

Therefore, in accordance with one aspect of the present invention, amethod of voltage modulation for computed tomography (CT) imaging isprovided. The method includes the steps of acquiring a set of EKGsignals having a plurality of triggering pulses and determining a periodof delay after each triggering pulse. The method further includes thestep of energizing a high frequency electromagnetic energy source to afirst voltage after each period of delay and acquiring a set of imagingdata of a scan subject while the high frequency electromagnetic energysource is energized to the first voltage. After acquiring a set ofimaging data, the high frequency electromagnetic energy source is thenenergized to a second voltage until a period of delay after a nexttriggering pulse.

In accordance with another aspect of the present invention, a radiationemitting imaging system includes a high frequency electromagnetic energyprojection source configured to project high frequency energy toward ascan subject. The system also includes a detector assembly configured toreceive high frequency electromagnetic energy attenuated by the scansubject and output a plurality of electrical signals indicative of theattenuation to a data acquisition system. The system further includes acontrol configured to determine a plurality of primary data acquisitionstages and a plurality of secondary acquisition stages. The control isfurther configured to energize the high frequency electromagnetic energyprojection source to a first voltage during each data acquisition stageto acquire imaging data. The control is also configured to energize thehigh frequency electromagnetic energy projection source to a secondvoltage during each secondary acquisition stage. The control is alsoconfigured to reconstruct an image of a scan subject from the imagingdata acquired during each data acquisition stage.

In accordance with a further aspect of the present invention, a computerreadable storage medium having a computer program stored thereon andrepresenting a set of instructions is provided. The set of instructionswhen executed by a computer causes the computer to analyze a set ofcardiac motion signals acquired from a set of sensors affixed to a torsoregion of a scan subject. The set of instructions further causes thecomputer to determine from the set of cardiac motion signals a number ofprimary data acquisition stages and a number of secondary acquisitionstages. The computer is then caused to transmit a first voltagemodulation signal to a voltage source configured to energize an x-rayprojection source used to project x-rays to the scan subject for dataacquisition. The first voltage modulation signal is configured to drivethe voltage source to the first voltage during each data acquisitionstage. The computer is then caused to acquire a set of imaging data.Thereafter, the computer is caused to transmit a second voltagemodulation signal to the voltage source wherein the second voltagemodulation signal is configured to drive the voltage source to a secondvoltage for each secondary acquisition stage.

Various other features, objects and advantages of the present inventionwill be made apparent from the following detailed description and thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate one preferred embodiment presently contemplatedfor carrying out the invention.

In the drawings:

FIG. 1 is a perspective view of a CT imaging system incorporating thepresent invention.

FIG. 2 is a perspective block schematic diagram of the systemillustrated in FIG. 1.

FIG. 3 is a pictorial view of a CT system for use with a non-invasivepackage inspection system.

FIG. 4 is a flow chart showing a process in accordance with oneembodiment of the present invention.

FIG. 5 is a representative cardiac data signal and a voltage modulationsignal superimposed thereon to illustrate application of that set forthin FIG. 4.

DETAILED DESCRIPTION

The present invention is direct to a system and method for acquiringimaging data of a scan subject using voltage modulation to reduce x-rayexposure to the scan subject. The present invention will be describedwith respect to a computed tomography system, but one skilled in the artwill readily appreciate that the present invention is also applicable toother radiation emitting imaging systems. Furthermore, the presentinvention will be described with respect to a “third generation” CTsystem. However, the present invention is also applicable with second orfourth generation CT systems. Additionally, the present invention willbe described with respect to the detection and conversion of x-rays, butone skilled in the art will readily appreciate that the presentinvention is also applicable with the detection and conversion of otherhigh frequency electromagnetic energy including gamma rays.

Referring to FIGS. 1 and 2, an exemplary computed tomography (CT)imaging system 10 is shown as including a gantry 12 representative of a“third generation” CT scanner. Gantry 12 has an x-ray source 14 thatprojects a beam of x-rays 16 toward a detector array 18 on the oppositeside of the gantry 12. Detector array 18 is formed by a plurality ofdetectors 20 which together sense the projected x-rays that pass througha medical patient 22. Each detector 20 produces an electrical signalthat represents the intensity of an impinging x-ray beam and hence theattenuated beam as it passes through the patient 22. During a scan toacquire x-ray projection data, gantry 12 and the components mountedthereon rotate about a center of rotation 24. Detector array 18 anddetectors 20 can be any number of high frequency electromagnetic energydetectors, such as gas-filled, scintillation cell-photodiode, andsemiconductor detectors as is know to those skilled in the art ofdetector design.

Rotation of gantry 12 and the operation of x-ray source 14 are governedby a control mechanism 26 of CT system 10. Control mechanism 26 includesan x-ray controller 28 that provides power and timing signals to anx-ray source 14 and a gantry motor controller 30 that controls therotational speed and position of gantry 12. A data acquisition system(DAS) 32 in control mechanism 26 samples analog data from detectors 20and converts the data to digital signals for subsequent processing. Animage reconstructor 34 receives sampled and digitized x-ray data fromDAS 32 and performs high-speed reconstruction. The reconstructed imageis applied as an input to a computer 36 which stores the image in a massstorage device 38.

Computer 36 also receives commands and scanning parameters, such aspatient size and task dependency, from an operator via console 40 thathas a keyboard for entering commands and scanning parameters. Anassociated cathode ray tube display 42 allows the operator to observethe reconstructed image and other data from computer 36. The operatorsupplied commands and parameters are used by computer 36 to providecontrol signals and information to DAS 32, x-ray controller 28 andgantry motor controller 30. In addition, computer 36 operates a tablespeed controller 44 which controls a variable speed table 46 duringimaging of a patient 22 within gantry 12. Particularly, table 46 isconfigured to move a patient 22 through a gantry opening 48 along anaxis 50, and may include a single or multiple speed settings.

In operation, a scan subject such as a medical patient 22 is positionedwithin the CT scanner or imaging device 10 on variable speed table 46with a selected region of the patient chosen for scanning adjacent tothe gantry 12. A technician or health-care operator inputs data into theoperator console 40, thereby defining a region-of interest (ROI) such asa cardiac region. The computer 36 then instructs the table speedcontroller 44 to move the table 46 towards the gantry opening 48 causingthe patient 22 to enter the gantry opening 48. Control mechanism 26causes x-ray controller 28 to provide power and timing signals to x-raysource 14 while the gantry motor controller 30 causes rotation of gantry12 to acquire imaging data of the patient 22 passing through the gantry12. Data acquired is then transmitted to DAS 32 in the form ofelectrical signals and image reconstructor 34 for digitalization andsubsequent image reconstruction. Computer 36 then processes thedigitized x-ray data to provide a reconstructed image of the ROI ondisplay 42.

Referring now to FIG. 3 and in accordance with an alternate embodimentof the present invention, a non-invasive package/baggage inspectionsystem 100 includes a rotatable gantry 102 having an opening 104 thereinthrough which packages or pieces of baggage may pass. The rotatablegantry 102 houses a high frequency electromagnetic energy source 106 aswell as a detector assembly 108. A conveyor system 110 is also providedand includes a conveyor belt 112 supported by structure 114 toautomatically and continuously pass packages or baggage pieces 116through opening 104 to be scanned. Objects 116 are fed through opening104 by conveyor belt 112, imaging data is then acquired, and theconveyor belt 112 removes the packages 116 from opening 104 in acontrolled and continuous manner. As a result, postal inspectors,baggage handlers, and other security personnel may non-invasivelyinspect the contents of packages 116 for explosives, knives, guns,contraband, etc.

Referring to FIG. 4, a flow chart illustrating the steps and actsassociated with an algorithm in accordance with the present invention isshown. The algorithm is initiated at 200 by a technician or CT scanneroperator who provides input to the computer at 202 related to patientdata such as sex, weight, and size. Generally, such operator-enteredinput includes a starting position and an ending position. A scan isinitiated at 204 which causes the patient to enter opening 48 of FIG. 1.Simultaneously therewith, a set of EKG signals are acquired at 206 froma set of EKG electrodes (not shown) affixed to a torso region of thepatient. The EKG signals detect motion signals including diastolic andsystolic phases of the cardiac region of the patient. The EKG signalsare acquired at 206 and transmitted to controller 26 or computer 36 foranalysis.

Upon reception of EKG signals at 206, a primary data acquisition stageand a secondary or non-data acquisition stage are determined at 208. Thestages are determined from trigger pulses found in the set of EKGsignals. A period of delay after each triggered pulse is then determinedat 209. A voltage modulation signal is then transmitted at 210 to thex-ray controller 28, FIG. 2, to cause a first voltage be applied to thex-ray source. That is, the x-ray source is energized to an “ON” state.The ON state is maintained for sufficient time to acquire imaging dataat 212. After the imaging data is acquired for that data acquisitionstage, a modulation signal is transmitted at 214 to the x-ray controllerto energize the x-ray source to a second voltage. The second voltagecorresponds to an “OFF” state thereby reducing x-ray emissions to thepatient. In one embodiment, the second voltage is a zero voltage.

The second voltage is maintained until another trigger in the set of EKGsignals is detected at 215. If a trigger is detected 217, the algorithmreturns to step 210 with the transmission of the first voltage signal todrive the x-ray source to a relative maximum voltage. If no othertriggers are detected 219, the algorithm continues to data processing at216 for subsequent image reconstruction at 218. The algorithm then endsat 220.

Preferably, during the secondary or non-data acquisition stage aspectral filter (not shown) is used to filter out any lower energyx-rays from the high frequency electromagnetic energy beam. Further, abowtie filter may also be implemented to reduce the range of intensityvalues received by the detector to also lower patient x-ray exposureduring the secondary or non-data acquisition stage.

The EKG signals acquired from the patient are used to establish animaging profile for the acquisition of imaging data. Pursuant to theimaging profile, the x-ray source is variably energized to modulate theprojection of x-rays toward the patient. Modulating the voltage appliedto the x-ray source allows for reduction of radiation exposure to thepatient during the secondary or non-data acquired stages by limitingx-ray emissions without allowing the filament of the x-ray tube to coolbeyond an acceptable level.

While EKG signals have heretofore been described as a means ofdeveloping an imaging profile, other data signals may be acquired andanalyzed to develop an imaging profile including respiratory datasignals.

Referring now to FIG. 5, the present invention will be describedschematically with respect to a cardiac motion signal and a voltagemodulation signal. As described previously, a cardiac motion signal 300is detected from a plurality of EKG sensors affixed to a torso region ofthe scan subject. The EKG signal 300 corresponds to the systolic anddiastolic phases of the scan subject's cardiac phases. Signal 300includes a number of triggering pulses 302 that correspond to thebeginning of each diastolic-systolic phase combination. That is, betweensuccessive triggering pulses 302, includes a single diastolic phase anda single systolic phase.

Also shown in FIG. 5 superimposed over EKG signal 300 is a voltagemodulation signal 308 corresponding to the voltage applied to the x-raytube of the imaging system. Voltage signal 308 is shown as superimposedover EKG signal 300 to illustrate the modulation of tube voltage withrespect to the triggering pulses 302 of EKG signal 300. The highs andlows of the voltage signal 308 do not correspond to any particularvoltage but illustrate a maximum and minimum voltage as a function oftotal voltage. As shown, tube voltage remains at a general minimum 310until after a triggering pulse 302 followed by a predetermined delay312. After the delay 312, the voltage as indicated by voltage signal 308is driven to a relative maximum 314. The relative maximum voltage 314 ismaintained until sufficient data is acquired for image reconstruction.That is, the relative maximum voltage 314 energizes the x-ray projectsource or tube to emit x-rays toward the scan subject for subsequentdata acquisition. Once sufficient data has been acquired for imagereconstruction, the tube voltage returns to a relative minimum 310thereby reducing the x-ray emissions of the x-ray projection sourceuntil the tube voltage is once again driven to a relative maximum. Asshown, the tube voltage will be driven to the relative maximum when asecond triggering pulse 302 is detected and the requisite period ofdelay 312 has passed.

The present invention has been described with respect to the acquisitionof imaging data using EKG signals to modulate tube voltage during thedata acquisition to reduce x-ray emissions to the scan subject. The EKGsignals are analyzed to determine an imaging profile and pursuant tothat imaging profile a primary data acquisition stage and a secondary ornon-data acquisition stage are determined. The primary data acquisitionstage corresponds to a high voltage being applied to the projectionsource and the secondary or non-data acquisition stage corresponds to alower voltage being applied to the x-ray projection source. Preferably,zero voltage is provided to the x-ray projection source during thenon-data acquisition stage.

Therefore, in accordance with one embodiment of the present invention, amethod of voltage modulation for computed tomography (CT) imaging isprovided. The method includes the steps of acquiring a set of EKGsignals having a plurality of triggering pulses and determining a periodof delay after each triggering pulse. The method further includes thestep of energizing a high frequency electromagnetic energy source to afirst voltage after each period of delay and acquiring a set of imagingdata of a scan subject while the high frequency electromagnetic energysource is energized to the first voltage. After acquiring a set ofimaging data, the high frequency electromagnetic energy source is thenenergized to a second voltage until a period of delay after a nexttriggering pulse.

In accordance with another embodiment of the present invention, aradiation emitting imaging system includes a high frequencyelectromagnetic energy projection source configured to project highfrequency energy toward a scan subject. The system also includes adetector assembly configured to receive high frequency electromagneticenergy attenuated by the scan subject and output a plurality ofelectrical signals indicative of the attenuation to a data acquisitionsystem. The system further includes a control configured to determine aplurality of primary data acquisition stages and a plurality ofsecondary or non-data acquisition stages. The control is furtherconfigured to energize the high frequency electromagnetic energyprojection source to a first voltage during each primary dataacquisition stage to acquire imaging data. The control is alsoconfigured to energize the high frequency electromagnetic energyprojection source to a second voltage during each secondary or non-dataacquisition stage. The control is also configured to reconstruct animage of a scan subject from the imaging data acquired during each dataacquisition stage.

In accordance with a further embodiment of the present invention, acomputer readable storage medium having a computer program storedthereon and representing a set of instructions is provided. The set ofinstructions when executed by a computer causes the computer to analyzea set of cardiac motion signals acquired from a set of sensors affixedto a torso region of a scan subject. The set of instructions furthercauses the computer to determine from the set of cardiac motion signalsa number of data acquisition stages and a number of non-data acquisitionstages. The computer is then caused to transmit a first voltagemodulation signal to a voltage source configured to energize an x-rayprojection source used to project x-rays to the scan subject for dataacquisition. The first voltage modulation signal is configured to drivethe voltage source to the first voltage during each primary dataacquisition stage. The computer is then caused to acquire a set ofimaging data. Thereafter, the computer is caused to transmit a secondvoltage modulation signal to the voltage source wherein the secondvoltage modulation signal is configured to drive the voltage source to asecond voltage for each secondary or non-data acquisition stage.

The present invention has been described in terms of the preferredembodiment, and it is recognized that equivalents, alternatives, andmodifications, aside from those expressly stated, are possible andwithin the scope of the appending claims.

What is claimed is:
 1. A method of voltage modulation for computedtomography (CT) imaging comprising the steps of: acquiring a set ofcardiac signals having a plurality of triggering pulses; determining aperiod of delay after each triggering pulse; after each period of delay,energizing a high frequency electromagnetic energy source to a dataacquisition voltage; acquiring a set of imaging data of a scan subject;and after acquiring the set of imaging data, energizing the highfrequency electromagnetic energy source to a non-data acquisitionvoltage until the period of delay after a next triggering pulse.
 2. Themethod of claim 1 wherein the non-data acquisition voltage is less thanthe data acquisition voltage.
 3. The method of claim 1 furthercomprising the steps of: determining a primary and a secondary imagingstage from the set of cardiac signals; energizing the high frequencyelectromagnetic energy projection source to the data acquisition duringthe primary imaging stage; and energizing the high frequencyelectromagnetic energy projection source to the non-data acquisitionvoltage during the secondary imaging stage.
 4. The method of claim 3further comprising the step of filtering low energy high frequencyelectromagnetic energy projected to the scan subject to reduce highfrequency electromagnetic energy exposure to the scan subject.
 5. Themethod of claim 1 further comprising the step of determining a radiationdosage profile from the set of cardiac signals.
 6. A radiation emittingimaging system comprising: a high frequency electromagnetic energyprojection source configured to project high frequency energy toward ascan subject; a detector assembly to receive high frequencyelectromagnetic energy attenuated by the scan subject and output aplurality of electrical signals indicative of the attenuation to a dataacquisition system (DAS); a control configured to: determine a primarydata acquisition stage and a secondary data acquisition stage for an R-Rinterval, the primary data acquisition stage beginning after atriggering pulse and the secondary data acquisition stage occurringafter the primary data acquisition stage and ending before a nexttriggering pulse of a next R-R interval; energize the high frequencyelectromagnetic energy projection source to a first voltage during theprimary data acquisition stage to acquire primary imaging data; energizethe high frequency electromagnetic energy projection source to a secondvoltage different from the first voltage during the secondary dataacquisition stage to acquire secondary imaging data; and reconstruct animage of the scan subject from imaging data acquired during each dataacquisition stage.
 7. The system of claim 6 further comprising a bowtiefilter configured to filter a portion of the nigh frequencyelectromagnetic energy projected by the high frequency electromagneticenergy projection source to the scan subject.
 8. The system of claim 6further comprising a plurality of EKG sensors configured to acquire aset of EKG signals of a cardiac region of the scan subject.
 9. Thesystem of claim 8 wherein the control is further configured to determinethe primary data acquisition stage and the secondary data acquisitionstage from the set of EKG signals.
 10. The system of claim 9 wherein thecontrol is further comprised to determine a number of subsets from theset of EKG signals and determine a triggering pulse within each subsetand energize the high frequency electromagnetic energy projection sourceto the first voltage after a delay of the triggering pulse.
 11. Acomputer readable storage medium having a computer program storedthereon and representing a set of instructions that when executed by acomputer causes the computer to: analyze a set of cardiac motion signalsacquired from a set of EKG sensors from a torso region of a scansubject; determine from the set of cardiac motion signals a number ofprimary data acquisition stages and a number of secondary acquisitionstages, wherein each secondary acquisition stage follows a primary dataacquisition stage and wherein each primary data acquisition stage occursentirely within a respective single R—R interval: transmit a firstvoltage modulation signal to a voltage source configured to energize anx-ray projection source used to project x-rays to the scan subject fordata acquisition, the first voltage modulation signal configured toenergize the voltage source to a first voltage for each primary dataacquisition stage; acquire a set of imaging data; and transmit a secondvoltage modulation signal to the voltage source, the second voltagemodulation signal being configured to energize the voltage source to asecond voltage for each secondary acquisition stage, the second voltagebeing less than the first voltage.
 12. The computer readable storagemedium of claim 11 wherein the set of instructions further causes thecomputer to determine a dosage profile from the set of EKG signals andmodulate the voltage source according to the dosage profile.
 13. Thecomputer readable storage medium of claim 11 wherein the set ofinstructions further causes the computer to reduce x-ray projections tothe scan subject during the number of secondary acquisition stages. 14.The computer readable storage medium of claim 11 wherein the set ofinstructions further causes the computer to determine the first voltagefrom a set of imaging parameters on a per imaging session basis.
 15. Thecomputer readable storage medium of claim 11 wherein the number ofsecondary acquisition states includes a number of non-data acquisitionstages.
 16. A method of cardiac CT imaging comprising the steps of:acquiring a series of cardiac signals defining a number of cardiaccycles each cardiac cycle defined by successive R pulses; determining aprimely acquisition period that begins after a first R pulse of acardiac cycle and a secondary acquisition period that occurs after theprimary acquisition period and begins before a second R pulse of thecardiac cycle for the number of cardiac cycles; energizing an x-raysource to a default, non-zero voltage; initiating CT data acquisitionfor the number of cardiac cycles; energizing the x-ray source to aprimary voltage that exceeds the default, non-zero voltage during CTdata acquisition for the primary acquisition period; and returning thex-ray source to the default, non-zero voltage during CT data acquisitionfor the secondary acquisition period.
 17. The method of claim 16 whereinthe primary voltage includes a maximum voltage.
 18. A radiation emittingimaging system comprising: a high frequency electromagnetic energyprojection source configured to project high frequency energy toward ascan subject; a detector assembly to receive high frequencyelectromagnetic energy attenuated by the scan subject and output aplurality of electrical signals indicative of the attenuation to a dataacquisition system (DAS); a control configured to: model dataacquisition for a heart of the scan subject based on a series of cardiacsignals defining a number of cardiac cycles of the heart, each cardiaccycle defined by a first R pulse end a second R pulse: apply a firstvoltage to the high frequency electromagnetic energy projection sourcebetween the first and the second R pulses of each cardiac cycle; acquireimaging data of the heart with the high frequency electromagnetic energyprojection source at the first voltage; thereafter apply a secondvoltage to the high frequency electromagnetic energy projection source,wherein said application of the second voltage occurs before the secondR pulse of a current cardiac cycle, the first voltage exceeding thesecond voltage; and reconstruct an image of the scan subject formultiple phases of each cardiac cycle.
 19. The system of claim 18wherein the second voltage includes a default voltage and the firstvoltage includes a maximum voltage.
 20. The system of claim 19 whereinthe default voltage includes a minimum voltage required to acquire data.